Books are shelved in general subject categories using the Library of Congress classification system. You may want to supplement your use of the catalog book search with browsing shelf areas for your topic.
Books on Civil War-related history are shelved on the library's upper level. Many books are found within the E section, broadly E441 through E668..
For Specific Areas:
E441-453: Slavery in the United States. Antislavery movements
E456-655: Civil War period, 1861-65
E456-459: Lincoln's admin.
E461-655: The Civil War, 1861-65
E482-489: Confederate States
E491-586: Armies. Troops
E591-600: Naval history
E666-670: Johnson's admin
E668: Reconstruction, 1865-77